1. Field of the Invention
The invention relates to catalytic converters. More particularly, the invention relates to optimizing back pressure in short plenum catalytic converters.
2. Prior Art
Traditionally, catalytic converters have had enough room under the vehicle to optimize plenum length for the application. A pair of plenums are important in a catalytic converter to let exhaust gasses from a relatively small diameter inlet pipe expand to flow through the catalyst channels and contract at the other end of the catalyst to enter the relatively small diameter outlet tube. A 50% split of the total plenum length (inlet plus outlet) between the inlet and outlet sides of the catalytic converter has been the standard for many years. Fifty percent of the total plenum length on the inlet side of the catalytic converter and fifty percent of the total plenum length on the outlet side of the catalytic converter is very effective as long as the total length can be engineered essentially without restriction. Commonly 80 millimeters or more has been used with a 50/50 split. This requires both that sufficient space is available and that materials cost allows for a longer converter.
With increasingly smaller cars having less room for catalytic converters and tighter control on materials cost, the plenum length must be reduced in newer vehicles. With reduced plenum lengths, back pressure is increased which can be significant in wide open throttle conditions relative to total horsepower and torque available in the drive train of the automobile. Equal plenum length, however, remains the standard.
An object of the invention is to reduce back pressure in a catalytic converter having a short total plenum length.
It is another object of the invention to reduce total cost for producing a catalytic converter through reduction of materials.
It is yet another object of the invention to produce a catalytic converter maintaining a high catalyst efficiency.
Advantageously, the particular construction of the invention employing unequal length input and output plenums in a catalytic converter accomplishes the foregoing objects of the invention.
Advantageously, according to a preferred example, this invention provides a catalytic converter of the type having an inlet plenum between a converter inlet and an axial inlet face of a substrate and an outlet plenum between a converter outlet and an axial outlet face of the substrate, wherein a first axial length of the inlet plenum is in a range of 20-40% of the first axial length of the inlet plenum summed with a second axial length of the outlet plenum to minimize flow resistance in said catalytic converter.